A variety of industrial facilities have experienced a need for a crane structure having the positive manipular lifting facility and maneuvering flexibility of conventional backhoe machines. For example, such rugged crane devices may be employed with a grapple or electromagnet to move scrap material and the like from place to place, for example from storage regions into trucks, etc. Backhoe machines generally are configured incorporating a motorized maneuverable platform which additionally is pivotal about a vertical axis. The platform generally supports an operator cab, a power supply and an articulated boom assembly that includes a boom component with an inboard end pivotally coupled to the platform and having a generally angulate form to facilitate the digging function as well as a gib or outer boom pivotally coupled to the outboard end of the boom component which is conventionally referred to by operators as the "stick". The boom component is driven vertically about its inboard pivot by a hydraulic cylinder arrangement coupled between the platform and a lifting point or bearing position which is traditionally located near the angular transition or "dog leg" curve of the boom at about the mid position between the top and bottom surfaces thereof. The stick typically is driven about its pivotal connection by a hydraulic assembly extending between the stick and the boom.
Approaches for retro-fitting a backhoe to provide a crane function generally have involved techniques for effecting some straightening of the boom component. U.S. Pat. No. 4,105,151 describes one technique wherein a wedge shaped portion of the boom is cut from its top surface, leaving the bottom plate or bottom surface intact. The upper portion of the boom then is bent about the apex of the thus-formed wedge-shaped gap until the exposed edges of the side pieces and top are in contact, whereupon the assemblage is welded. The result is a shortening of the boom and the evolution of a compound curve therein.
A more popular conversion approach is described in U.S. Pat. No. 4,247,035 which provides a technique wherein a wedge form portion of the boom just above the angular transition or dog leg is removed and the upper portion thereof is bent about the top plate whereupon an insert conforming to the resultant gap is welded into the assemblage. This arrangement continues the compound curvature of the boom but provides a slight improvement in the overall reach or height made available with the resultant lifting boom. The arrangement, however, has been observed to, in effect, maneuver the lifting point or bearing position for hydraulic cylinder connection to a location proximate the upper surface of the restructured boom. As a consequence, the structural integrity of the boom has been affected resulting from time to time in breakage which, in turn, has led to further buttressing or build-up of steel surfaces about the point of compound transition or curvature. of the boom. The resultant length of this more popular retrofit arrangement still has not been found adequate. While the overall height of the articulated structure may be lengthened by increasing the length of the stick component, this expedient becomes undesirable for manipulative operations wherein the stick is withdrawn to its platform to an essentially vertical orientation suspended above ground level. For such orientations, a clearance of the stick and to the ground must be sufficient to elevate such implements as grapples and the like above the surface of the ground. For larger such implements, this clearance is insufficient for manipulation near the crane platform.